The invention relates generally to a ground fault detection system and methods for ground fault detection.
A wide range of equipment, such as electric motor drives, are known and are in use for a variety of applications, such as in factory automation systems, power generation systems and so forth. Typically a load is connected to a power source, such as a drive in the case of a motor, which provides electrical power to the load in a controlled manner. In alternating current (AC) motor drive systems, for example, electrical power is converted from an AC power source into direct current (DC) voltage. The DC voltage is then converted via an inverter into AC voltage with controlled frequency and amplitude which may be applied to drive the electric motor. Other loads are provided with power in similar ways, with converters of various types providing controlled frequency AC power, either at a fixed frequency or a controlled variable frequency (e.g., for regulating the rotational speed of a motor).
It is often desirable to detect ground faults in such systems to prevent damage of the components as well as time-consuming equipment unavailability in the case of failure due to short circuiting, and other failure causes detectable from ground fault information. One way of detecting ground faults is by using a DC link choke with a pair of inductors and one or more windings for ground fault detection. Typically, the inductors on the primary current paths filter the primary DC currents. Further, ground fault is detected by comparing currents from each path. A ground fault may have occurred if substantially high current leaks into ground instead of the load.
However, existing ground fault detection circuits may have undesirable effects. For example, some systems rely on a large number of inductors and windings that may increase the size and associated material, shipping and storage costs. Moreover, depending upon the circuit and physical winding design, unwanted spikes in current may occur that, in some cases, may be fed back to upstream circuitry (such as rectifier and other components) to its detriment.
Accordingly, it would be desirable to develop a ground fault detection system that detects ground faults while preventing excessive voltage stress in such systems.